1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition and a piezoelectric element composed of the piezoelectric ceramic composition.
2. Description of the Related Art
Piezoelectric ceramic compositions have hitherto been widely used as materials for piezoelectric elements, for example, piezoelectric vibrators, piezoelectric resonators, piezoelectric filters and piezoelectric oscillators. The piezoelectric ceramic compositions have been required to have varying characteristics depending on the end use application. For example, regarding oscillators, Qm values of the piezoelectric ceramic compositions are required to be high in order to oscillate and temperature coefficients of frequencies are required to be even in order to maintain reliability.
Regarding a conventional piezoelectric ceramic composition, in Japanese Examined Patent Application Publication No. 47-9185, disclosed as a Pb{(Mn⅓Nb⅔)ZrTi}O3xe2x80x94based material having a perovskite structure and represented by a general chemical formula ABO3 is Pb(Mn⅓Nb⅔)O3xe2x80x94PbTiO3xe2x80x94PbZrO3, to which small quantities of at least one oxide selected from the group consisting of MnO2, CoO and NiO was added.
In order to meet high frequencies, the reduction of piezoelectric element thickness has been accelerated. As a consequence, the requirements for high strength materials in which cracks and chips are not likely to occur during working, even if the thicknesses are reduced, have been intensified.
However, a Pb{(Mn⅓Nb⅔)ZrTi} O3xe2x80x94based material in which the quantity of Pb in A site of the perovskite formula is stoichiometric, the Pb amount is 1.00 mol, so that the flexural strength is as low as 110 to 130 MPa. Therefore, fracture is likely to occur due to shocks during the work of reducing thickness or making an element.
Accordingly, it is an object of the present invention to provide a piezoelectric ceramic composition and a piezoelectric element having superior shock resistance in which cracks and chips are not likely to occur during working, even if the thicknesses are reduced.
In order to achieve the aforementioned objects, according to a first aspect of the present invention, a piezoelectric ceramic composition containing a complex oxide having a perovskite structure, as a primary component, which is composed of at least Pb, Zr, Ti, Mn, Nb and O, and is represented by a general chemical formula ABO3, is provided. In the piezoelectric ceramic composition, the total molar quantity of elements constituting A in the aforementioned formula representing the primary component is smaller than the total molar quantity of elements constituting B in the formula representing the primary component, and Si is added as a secondary component with the content of about 0.010 wt % to 0.090 wt %, in terms of SiO2, relative to the primary component.
In the piezoelectric ceramic composition, the ratio of the total molar quantity of elements constituting A in the formula representing the primary component to the total molar quantity of elements constituting B in the formula representing the primary component is preferably about 0.985 to 0.998.
The piezoelectric ceramic composition according to the aforementioned configuration has a flexural strength of about 150 MPa or more, and even if the thickness is reduced, cracks and chips are not likely to occur during working.
According to a second aspect of the present invention, a piezoelectric ceramic composition represented by a compositional formula Pba {(Mn⅓Nb⅔)xZryTiz}O3+b wt % MnO2 +c wt % SiO2, is provided, wherein a, b, c, x, y and z are 0.985 xe2x89xa6axe2x89xa60.998, 0.155xe2x89xa6b xe2x89xa60.500, 0.010xe2x89xa6cxe2x89xa60.090, 0.045xe2x89xa6xxe2x89xa60.200, 0.290xe2x89xa6yxe2x89xa60.425, 0.475xe2x89xa6zxe2x89xa60.580 and x+y+z=1.
The piezoelectric ceramic composition according to the aforementioned configuration has a flexural strength of about 150 MPa or more, and has a Qm value necessary for piezoelectric vibrators, piezoelectric resonators, piezoelectric filters, piezoelectric oscillators, etc. Furthermore, an arbitrary temperature coefficient of resonant frequency can be achieved.
According to a third aspect of the present invention, a piezoelectric element is provided with a base material composed of the aforementioned piezoelectric ceramic composition and electrodes formed on the top and bottom faces of the base material.